The invention relates to a method for the production-optimized operation of a horizontal strip casting facility, and a horizontal strip casting facility for carrying out the method.
A conventional horizontal strip casting facility for producing a metal strip to be wound into a coil comprises a furnace (holding furnace or hot-top), onto the exit opening of which is flanged a cooled mold whose mold outlet determines the cross section of the metal strip.
A withdrawal unit is arranged at a distance from the mold. The metal strip is guided in a horizontal direction through the withdrawal unit between several horizontally extending withdrawal rollers.
From the withdrawal unit, the metal strip is guided further in a horizontal plane to a curling unit. The curling unit is equipped with several coiling rollers which bend the metal strip so that after emerging from the curling unit it curls up into a coil.
Located between the withdrawal unit and the curling unit, usually in the vicinity of the withdrawal unit, is a strip cutting unit that is displace able in roller-supported fashion in the longitudinal direction of the metal strip, and cuts through the metal strip when a coil has reached its predetermined diameter.
If necessary, a milling unit for machining the surface of the metal strip can also be integrated between the withdrawal unit and the curling unit.
The movements of the withdrawal rollers of the withdrawal unit, the strip cutting unit, and the coiling rollers of the curling unit are generally coupled to one another via a stored-program control system or via the cast metal strip.
In order to ascertain the temperature status and thereby the quality of a metal strip leaving the mold, it is known to measure the temperature of the metal strip directly after the mold, continuously or from time to time, by way of a contact pyrometer, optical pyrometer, or infrared beams. This measurement is only single-point, however, and is performed predominantly in the center of the metal strip. From these temperature values, usually displayed in digital or analog fashion, conclusions are then drawn as to the temperature status of the entire metal strip. A measurement of this kind thus allows only rough conclusions as to the general temperature level of the cast metal strip. Short-term local temperature anomalies can therefore not be detected in most cases. Such anomalies result, however, in melt perforations with resulting severe damage to the horizontal strip casting facility, or holes or cracks in the metal strip, or other strip defects. The known method thus provides no information as to the temperature distribution over the entire width of the metal strip. Holes or cracks in the metal strip can consequently also be detected only by chance. Using the known methods it is moreover not possible to ensure that the coils which are ultimately wound are of suitable quality. Deficiencies in the quality of the products produced from the coils cannot be ruled out.
Improving upon known approaches, it is the object of the invention to provide a method for production-optimized operation of a horizontal strip casting facility, and a horizontal strip casting facility for carrying out the method. The invention ensures that the operator of the horizontal strip casting facility is informed, at every point in time during casting, of the surface temperature profile, and thus the condition, of the metal strip.
The invention teaches a method for optimizing the operation of a horizontal strip casting facility for producing metal strip in which metal strip is withdrawn from a watercooled mold that is adjacent a temperature-controlled furnace. The metal strip that emerges from the mold is continuously scanned in a fan shape across the width of the strip with an infrared scanner that is spaced from the strip immediately after the strip emerges from the mold, so as to determine the temperature profile of the strip. These temperature values are passed to a computer, where they are processed and, along with emissivity values corresponding to the material being cast, are used to generate a graphical representation of the temperature profile that is displayed to the operator on a monitor. This profile information is used to control a number of parameters relating to the operation of the facility, including the speed of the metal strip, the quantity of cooling water that is fed to the mold, withdrawal parameters, and the melt temperature in the furnace.
According to a further aspect of the invention, when the temperature goes above or below predefined upper or lower temperature limit values, the computer triggers an alarm or brings about a shutdown of the horizontal strip casting facility.
A primary aspect of the invention is the positioning of an infrared scanner, operating in noncontact fashion, directly at the mold outlet. Because the temperature measurement head of the infrared scanner is movable, the entire width of the metal strip can be scanned in a fan shape. Scanning is preferably accomplished up to approximately ten times per second. The temperature values ascertained by the infrared scanner are then conveyed to a computer, taking into account the emissivity values corresponding to the material being cast. On the basis of the temperature values, the computer then creates either a color-graded graphic diagram or a temperature profile diagram depicting the temperature over the width of the metal strip. These diagrams can then be selectably displayed on a monitor, in succession or next to one another, or even on two separate monitors. Based on the curves in the diagrams, the operator of the horizontal strip casting facility immediately recognizes critical situations and can therefore also immediately react and make appropriate adjustments.
A particular advantage of this approach is that because the instantaneous temperature profile is known, the horizontal strip casting facility can always be operated with the maximum possible production output. In other words, the strip speed, volumes of cooling water to the mold, withdrawal parameters, and melt temperature can each be specifically controlled.
In this context, a very important advantage of the invention lies in its ability to accurately depict to the operator the relative state of the solidification zone, which hitherto was not provided to the operator.
Since the computer is capable of detecting temperature anomalies over the entire width of the metal strip, a further advantage in the context of the invention is the fact that if the temperature goes above or below predefined upper and lower limit values, the computer can trigger an alarm or even bring about a shutdown of the horizontal strip casting facility. For this purpose, the computer is coupled to the withdrawal unit via a stored-program control system.
If an excessively high temperature is detected, for example, the computer can trigger an alarm with delayed shutdown, so that the operator can in any case still react and take suitable measures to normalize the temperature. If, however, the computer detects a considerable decrease in temperature or even a breakage, it shuts down the entire horizontal strip casting facility. A more serious production malfunction can thereby be prevented.
It is also within the scope of the invention to analyze the causes of temperature fluctuations at a later point in time, since the computer stores all the data and consequently provides documentation that can be examined later.